查看更多>>摘要：? 2022 Elsevier B.V.Phosphates of Ca8ZnLn(PO4)7 (Ln3+ = La – Nd, Sm – Lu) with β-Ca3(PO4)2-type structure were prepared by high-temperature solid-state technique on air. All compounds of Ca8ZnLn(PO4)7 are centrosymmetric and have R3ˉc space group, which has been proved by several methods such as second-harmonic generation, dielectric spectroscopy, and Rietveld analysis. The influence of Ln3+ on the structure, luminescent properties and temperature of phase transitions, which corresponds with “tetrad” effect, has been investigated. The bandgap width and location of 4f Ln3+ and Ln2+ levels relatively to the energy bands were determined using the data of luminescent spectroscopy.
查看更多>>摘要：? 2022 Elsevier B.V.The phase equilibria including the isothermal sections at 1100 and 1300 °C as well as the liquidus surface projection of the Hf–Si–V ternary system were experimentally determined. The microstructures, crystal structures and phase constitutions of the annealed and the as-cast alloys in whole composition range were investigated by means of scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction and electron probe microanalysis, respectively. The isothermal sections of the Hf–Si–V system at 1100 and 1300 °C were accordingly constructed. Fifteen three-phase regions were confirmed, the ternary compound HfVSi was identified, and the solubilities of the third element in the binary compounds were determined. In the meanwhile, based on the XRD data obtained in the present work and by means of the JADE software package, the lattice parameters of each compound are calculated. Furthermore, the solidification paths of the Hf–Si–V as-cast alloys were analyzed to verify the primarily solidified phases from the liquid phase. Fifteen primary solidification regions were finally confirmed in the liquidus surface projection. Particularly, transmission electron microscopy results revealed that the binary stoichiometric compound V6Si5 extended into the Hf–Si–V ternary system, forming the line compound (V,Hf)6Si5. With the decrease of temperature, the line compound (V,Hf)6Si5 can decompose into two phases, one of which V(Hf)6Si5 has the composition near V6Si5, another near Hf2V4Si5, but with the same structure type. The Hf2V4Si5 phase is proposed to form due to the miscibility gap of the line compound (V,Hf)6Si5. The present experimental results are useful for the thermodynamic assessment of the Hf–Si–V ternary system, and the database development for the Nb/Mo–Si–V–Hf containing multi-component superalloy materials.
查看更多>>摘要：? 2022 Elsevier B.V.Secondary phases in bulk metallic samples are difficult to characterize by conventional X-ray diffraction because the diffracted intensities are dominated by the contribution of the bulk material. Electron diffraction provides a better spatial resolution and one can obtain single crystal diffraction data from submicron sized precipitates. In this work we show that 3D electron diffraction tomography can yield diffraction data sets suitable for ab initio structure solution. We apply the recently proposed low-dose electron diffraction tomography method to 3 different phases in Al-based alloys: θ’-Al2Cu, Al6Fe and Al4.5FeSi. The structures of these phases were unambiguously determined even though there are other phases with similar chemical compositions and EDS analysis is not sufficient to distinguish them.
查看更多>>摘要：? 2022 Elsevier B.V.Apparent elastic and anelastic properties of the martensitic phase of Ni55Fe18Ga27 single crystals have been studied after different heat treatments over wide ranges of temperatures (13–370 K) and strain amplitudes (5 × 10-8–10-5) at frequencies near 100 kHz. These properties depend crucially on the heat treatment because of strong pinning of twin boundaries by quenched-in point defects. Two stages are revealed in the temperature dependence of the effective Young's modulus and anelastic properties of the alloy that can be associated with pinning/depinning of twin boundaries by/from different types of point defects, most likely vacancies and divacancies. Experimental data evidence that diffusion of the vacancy-type defects in the temperature range under study is predominantly defect-assisted, enhanced by twin boundaries.
查看更多>>摘要：? 2022 Elsevier B.V.Polymer-based composite electromagnetic interference (EMI) shielding materials have aroused great interest among scientific researchers because of excellent properties. Herein, the poly(vinylidene fluoride) (PVDF)-carbon nanotube (CNT)-Graphene (G)-NiCo chains composite film with ultrahigh EMI shielding properties was prepared through solution mixing and compression molding. In the composite film, 1D carbon nanotube (CNT) and NiCo chains connected the surrounding 2D graphene nanoplates and formed interfacial interconnected networks. The electrical conductivity and total electromagnetic interference shielding effectiveness (EMI SET) of the samples increased progressively with the increased NiCo quality contents. The resultant PVDF-CNT-G-8NiCo composite film exhibited an excellent electrical conductivity of 9.12 S/cm and an ultrahigh EMI SET of 63.3 dB. The results were superior to those of PVDF-CNT-8NiCo composite film, clearly confirming the synergistic effect of graphene nanoplates and CNT. The formation of multi-layers interfacial conductive CNT-G-NiCo networks promoted conductive dissipation, multiple reflections and scattering of incident electromagnetic (EM) waves. Meanwhile, this work provides guidance for the rational design of high-performance polymer-based composite EMI shielding materials and has great potential in practical applications.
查看更多>>摘要：? 2022 Elsevier B.V.The dynamic mechanical behaviors of the as-extruded Mg-1Al-6Y alloy was investigated by using split Hopkinson pressure bar (SHPB) at strain rates of 587 s?1- 1986 s?1 and temperatures of 293–623 K. The results revealed that the microstructures and deformation mechanisms of the extruded alloy are sensitive to the strain rates and temperatures. The yield strength and compressive strength of the alloy are obviously improved with the increases of strain rate and weakened with increases of temperature. The experimental results demonstrated that the extension twinning and dislocation slips are the dominant deformation structures during the high strain rates impact. Temperatures have great influences on the dynamic mechanical behaviors of Mg-1Al-6Y. It is easy to form basal textures during the high-speed impact process of the alloy. A new constitutive model based on the Johnson-Cook model has been constructed to study the dynamic mechanical behaviors of the alloy. It is found that the new equation could accurately predict the flow stresses and deformation behaviors of the alloy under the slip-dominated condition.
查看更多>>摘要：? 2022 Elsevier B.V.This study uses the simple precipitation technique to develop a novel nanocomposite material comprised of samarium hydroxide nanorolls attached to the surface of graphitic carbon nitride nanosheets as active electrode materials for supercapacitors. The unique texture (morphology) of Sm(OH)3 nanorolls attached to the g-C3N4 nanosheets aid in creates a substantial number of active sites during redox reactions. Sm(OH)3/g-C3N4 nanocomposite exhibits a specific capacitance of 586 F g?1 at 1 A g?1 in 3 M LiOH, though its constituents Sm(OH)3 (227.87 Fg?1 at 1 A g?1) and g-C3N4 (135.55 Fg?1 at 1 Ag?1). Benefiting from its morphological structure, the prepared nanocomposite (SCN20) achieved a high cyclability of 97.5% even after 3000 continuous cycles and coulombic efficiency of 95.1%. Additionally, an asymmetric supercapacitor device was constructed by employing a positive electrode as Sm(OH)3/g-C3N4 nanocomposite (SCN20) and negative electrode as activated carbon (AC), which exhibits a high energy density of 37.23 W h kg?1 with the respective power density of 3.5 kW kg?1. This investigation is about the exciting morphology of the novel nanocomposites and their synergetic reaction existing between them, which bring forth the nanoengineering of as-synthesized active materials for the application in supercapacitors.
查看更多>>摘要：? 2022In the field of nanotechnology, the electrodes have received widespread attention as they are a key factor affecting the performance of lithium-ion batteries (LIBs). In this study, a cobalt niobate/reduced graphene oxide composite material (CoNb2O6/rGO) was prepared using ball-milling-assisted high-temperature calcination and used as an anode for LIBs for the first time. We studied the effects of calcination temperature on the morphology, structure, and electrochemical performance of CoNb2O6/rGO. The experimental results showed that rGO wrapped around the sphere-like CoNb2O6 particles of nanoscale size. With increasing calcination temperature, the crystallinity of CoNb2O6 increased, while the number of defects in rGO decreased, thus improving the conductivity of CoNb2O6/rGO. CoNb2O6 exhibits a higher specific capacity—the discharge capacity of CoNb2O6/rGO-900 is 540.9 mAh/g initially and 457.3 mAh/g after 200 cycles—than that exhibited by graphite (370 mAh/g) at low current densities (0.1 A/g). Furthermore, CoNb2O6 exhibits excellent cyclic stability—the discharge capacity is 130.6 mAh/g initially and 102.8 mAh/g after 4000 cycles, with a capacity retention rate of 78.7%—under a high current density of 5 A/g. The preparation method is a solid-phase technique suitable for large-scale preparation and industrial production.
查看更多>>摘要：? 2022 Elsevier B.V.Despite promising initial properties, the industrial applicability of magnetic shape memory alloys of the Ni-Mn-Ga family is distinctly limited by the temperature range it can operate in. Here we investigate the effects of minor substitutions of Fe for Ga on the thermodynamic, structural, and magnetic properties of Ni50Mn25FexGa25-x (3.0 < x < 7.5). Single crystals are essential for most intended applications, the studied compositions were prepared in single crystalline form. With increasing iron content, the melting point of the alloy decreases slightly from 1407(2) to 1394(2) K, while the structural B2’→L21 ordering transition increases in temperature from 1066(2) to 1082(4) K. Magnetisation measurements find that both the Curie temperature and the martensitic transformation temperature increase approximately linearly with Fe concentration, with Curie temperature increasing from 398(1) to 427(2) K, and martensitic transformation temperature increasing from 274(1) to 372(1) K when going from x = 3.0–7.5. The martensitic transformations above room temperature were confirmed by temperature-dependent single-crystal X-ray diffraction. These observations are compared with polycrystalline materials of the same series and support results of the previous studies. The shrinking gap between Curie and martensitic transformation temperatures, as well as the reduction in the low temperature saturated moment from 3.52(2) to 2.78(3) μB/f.u. make this substitution less industrially attractive but provide essential structural and property evolution details needed to improve and tune theoretical modelling of this important material family.
查看更多>>摘要：? 2022 Elsevier B.V.We introduce a new method for overcoming the strength–ductility trade-off by using a non-metallic alloying method, whereby numerous oxygen atoms are introduced in a conventional A356 alloy (I-A356 alloy). Self-organized nanofibers containing oxygen atoms formed in the melt had a chemically coherent interface with the matrix after solidification. Furthermore, the nanofibers (~10 nm in width) developed small sub-grains (<1 μm in size) with wide low-angle boundaries within the grains. Pre-existing dislocations developed by the small lattice mismatch between the nanofibers and matrix promoted strong activities. The sub-grain boundaries do the role of dislocation cells during plastic deformation, imparting high elongation to the I-A356 alloy. In addition, finely dispersed Si-rich nanoprecipitates formed during the aging treatment. The oxygen-rich intermixed layer at the Al–Si interfaces with a small radius of curvature drove Al–Si interdiffusion owing to the high attractive binding energy with Al. Thus, in addition to Mg2Si precipitates, the Si-rich nanoprecipitates further enhanced the alloy strength. Therefore, both, the ultimate tensile strength and elongation to failure of the I-A356 alloy, significantly increased by approximately 69.6 MPa and 14.8%, respectively, in relation to those of the A356 alloy.
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